Stretch bending machine and method



March 9, 1965 E. s. HOCKMAN ET AL 3,172,450

STRETCH BENDING MACHINE AND METHOD Filed Sept. 28. 1961 United States Patent 3,172,456 STRETCH BENDEN G MACHINE AND METHOD Elroy S. Hockman, Trenton, N.J., and Frederick Weidmann, Morrisville, Pa, assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Sept. 28, 1961, Ser. No. 141,478 8 Claims. (Cl. 72-131) This invention relates to forming bent workpieces, such as window frames, moldings, trim strips, etc. having a desired cross-section. Use is made of the well-known principle that spring-back of the bent workpiece can be eliminated by stretching or tensioning the workpiece beyond its elastic limit during bending.

Such stretch forming has been used heretofore in forming elongated bent workpieces wherein the bending of the stock is carried out by wrapping it lengthwise about a rotatable member having a peripheral surface of the configuration of the bent workpiece, but in all of these prior arrangements of which we are aware the stretching of the stock is accomplished by applying the tensile force with a fluid pressure operated cylinder and piston or equivalent device adapted to clamp the strip and resist its being drawn around the rotating member surface. Because of the necessity of having to stop the feed to clamp and unclamp the stock in such prior arrangements, the speed of producing bent workpieces thereby is less than desired.

Our invention enables continuous, i.e. uninterrupted, stretch forming of such bent workpieces from a strip of stock, and in its broadest concept is directed to feeding the stock strip through die means adapted to alter the initial cross-section of the strip to the cross-section desired for the workpieces, and wherein the resistance to passage of the strip through the die means serves as the reaction force in stretching the desired cross-section beyond its elastic limit in tension during the bending operation. The means by which the invention as carried out will be clearly understood from the following description of one specific embodiment thereof illustrating its application to forming channel-section frames for pivoted ventilator windows of automotive Vehicles, wherein:

FIGURE 1 is a schematic view showing the method and apparatus for forming such window frames in accordance with .the invention from strip continuously fed from coil stock.

FIGURE 2 is an enlarged perspective fragmentary view of one set of the strip clamping and serving means carried thereby.

FIGURE 3 is a perspective view of a completed bent window frame produced in accordance with the invention.

As shown in FIGURE 1, sheet metal strip stock 1 supplied from a coil 2 thereof is passed between die means indicated generally by the numeral 3 which alters the initial flat cross-section of the strip 1 to channel shaped cross-section strip 4. The channel shaped cross-section is that represented by the sides 5 and 6 and web 7 of the completed workpiece, or window frame 8 shown in FIGURE 3.

Strip 4, after passing the die means 3, is wrapped about a rotating bender member 9 whose peripheral surface 19 has a configuration of the bent workpiece don diametrically opposite sides of the member d. By rotating the member 9 with the strip 4 secured thereto, the strip 4 is bent to the same configuration as that of the peripheral surface 10 of the member, while pulling the strip 1 from the coil 2 through the die means 3.

While the die means 3 may take various forms depending upon the desired cross-section of the workpiece 8. the predetermined or initial cross-section of the stock strip 1 or its specific material, we have illustrated this die means schematically as comprising oppositely co acting rollers 11 and ii wherein the upper roller 11 has a peripheral groove 12 into which the lower roller 11 extends to define a generally channel-shaped passage for the fiat strip 1 being drawn therethrough by the rotation of the bending member 9. Suitable means, schematically illustrated by the adjusting screws 13, 13', are provided for adjusting the pressure imposed on the strip during its passage between the rollers. Such pressure must be adjusted to impose a resistance to passage of the strip therethrough with a force substantially equal to the elastic limit of the channel section strip 4 in tension. Preferably this pressure is adjusted to eifect such a resisting force slightly exceeding the tensile elastic limit of the strip 4, but in no case should resisting force exceed the ultimate strength of the strip 4 in tension. If the resisting force resulting solely from changing the flat section of the stock strip 1 to the channel section of strip 4 is insufiicient to provide the desired reaction or resisting force to enable the strip 4 being stressed beyond its tensile elastic limit by the rotation of the member d, the necessary additional pressure of the rollers 11 and 11' against the strip may be effected byadjusting t em toward each other by the means 13, 13'. While only a single pair of coacting rollers 11, fl is shown, it is contemplated that many stretch forming operations employing this invention will require progressive rolling of the stock strip 1, using a series of coacting sets of upper and lower rollers. Also, other means for altering the initial cross-section of the strip 1 to that of the desired cross-section of the strip 4 may be employed, such as wire-drawing type dies, or equivalent means.

The bending member 9 is mounted for rotation about the axis of its shaft 14 which may be suitably journaled in a fixed support 14 above a workpiece receiver bin 15. The means for rotating the bending member 9 is shown as a pulley 16 drivin the shaft is and connected by a flexible belt 1'7 through a slip clutch 18 to the shaft 19' of an electric motor 19. The slip clutch 18 should be selected to have a driving torque which will not exceed the maximum torque necessary to be applied by the rotating member 9 in stretching the channel section strip 4 beyond its elastic limit tension. In other words, because of the unequal radial distances of the peripheral surface 10 of the member from its shaft 14, there must be a varying speed of rotation of the member 9 in order to prevent the speed of its peripheral surface 16 over-stretching the channel section strip 4. Accordingly, when the radial distance of the strip 4 at its point of tangency with the peripheral surface it? is at a minimum from the shaft 16 there will be no slippage of the clutch 18, but as this radial distance increases the clutch will slip as necessary to avoid excessive stretching of the strip.

Means are provided for releasably securing or attaching the strip to the peripheral surface iii of the rotating member 9, and for severing the finally bent strip thereon in lengths required for the finished workpieces. In the arrangement shown, the releasable securing or attaching means takes the form of two clamps ill and 21 carried by the bending member 9 on diametrically opposite sides thereof as shown in FIGURE 1. Each of these clamps is movable by a fixed cam 22 on the support 14' to a first position, wherein the strip 4 is clamped to the peripheral surface it) of the member 9; and after approximately 270 of rotation of the member 9 the clamp is moved to its released position by a second fixed cam 23 on the support 14'. Adjacent the respective clamps 20 and 21 are strip shearing elements 24 and 25', which are also carried by the rotating member 9. Each of these shearing elements is actuatable by a cam 26, fixedto the support is, to shear the strip 4 on the bending surface ltl Patented Mar. 9, 1965 3 immediately following its adjacent clamp 24 or 21 being moved to its strip clamping position.

FIGURE 2 more clearly illustrates one of these sets of strip clamping and shearing means, wherein the clamp 24) is shown in the form of a pivoted cam follower arm 27, pivoted by a pin 28 to a bracket 29 fixed to the rotating member 9. During pivotal movement of the arm27 in the strip clamping direction, the actual clamping engagement with the strip is effected by a toggle link 30 which is also pivoted at one end to the bracket 29 by a pin 31. Adjacent its other end this link 30 is pivotally connected by a pin 32 to the other link 3-3 of the toggle which, in turn, is pivoted by a pin 34 to the arm 27. It is believed clear from inspection of FEGURE 2 that during movement of the arm 27 in a counterclockwise direction about its pivot 28 the toggle links 30, 33 will pivot into alignment with each other, in which position the movably pivoted end 35 of the toggle link 3i) will tightly clasp the strip 4 against the peripheral surface ll of the member 9, and will remain so until the arm 27 of the clamp is swung in the opposite or clockwise direction to release the strip 4.

The shearing means, as shown in FIGURE 2, is illus trated for simplicity as comprising merely a two-armed bell crank element 24 pivoted by a pin 36 to the bracket 29. At one end of this element is a strip shearing edge 37, and its other end carries a cam follower 38 which is adapted to rotate the element 24 in a counterclockwise direction about the pin 36 in response to passage over the fixed cam 26 (FIGURE 1). Return means in the form of a spring 39 may be provided to bias the shearing edge 37 of the element away from the strip 4 after each shearing operation.

In the continuous forming of the bent window frames, the bending member 9 is rotated continuously, but at varying rotational speeds as the result of slippage of the clutch 18 in maintaining a substantially constant peripheral speed of the bending surface If to avoid overstressing the channel section strip 4 beyond its tensile elastic limit. The flat strip stock 1 in passing between the rollers 11, 11 is altered in cross-section to the channel shaped crss-section desired for the workpiece 8, and the resistance imposed by the rollers to passage of the strip therebetween applies a sufficient tensile force during rotation of the member 9 to stress the channel section of the strip 4 to substantially, or somewhat in excess of, its elastic limit. The strip 4 extends generally tangentially to the peripheral surface of the rotating bending member 9 and is clamped thereto after each half cycle of rotation of the member 9 by one or the other of the clamps 20, 21 in passing over the cam 22. Immediately after such clamping, that portion of the strip which has been bent to its desired configuration by being wrapped around the surface 10 during the preceding half cycle of rotation is severed from the remainder of the strip by the shearing element 24 as it passes over its cam 26. Thence, after the particular clamp or 21 which is still retaining this severed portion of the strip to the bending surface has been tripped by the second fixed cam 23, the severed portion is released and falls into the receiving bin 15. If necessary, suitable ejecting means (not shown) may be added to insure disengagement of the severed bent portion or workpiece from the bending member 9 after the clamp has been released.

Continuous production of elongated bent workpieces from coiled strip stock is thus obtained in accordance with our invention. As each coil 2 is used up it may be united by welding to the outer end of a successive stock coil and the process continued indefinitely. By spacing the coil 2 a sufficient distance from the die means 3, such joining on of successive coils may be done with-- out interruption of the feed to the die means.

While only a single preferred embodiment of the invention has been disclosed, it is appreciated that numerous 4 minor changes may be made without departing from the V spirit and scope thereof as defined in the following claims.

We claim:

1. The method of forming successive elongated bent workpieces having a desired cross-section, comprising pulling a strip of stock'of other than said desired crossscction between two members cooperable in response to movement of said strip therebetween to alter the crosssection of the strip to said desired cross-section, applying sufficient force to said strip in opposition to said movement to stress said desired cross-section to substantially its elastic limit in tension, bending successive portions of strip which have passed between said members and while'they are under said tension to substantially their final configuration, and then relieving the successive bent portions of said tension and severing them from the strip. 2

2. The method of formingsuccessive elongated bent workpieces having a desired cross-section from a continuous strip of stock, comprising supplying said strip with an initial cross-section different from said desired cross-section but changeable to the latter by pulling through die means whose compressive force on the strip required to effect said desired cross-section does not resist passage of the strip therethrough with sufficient force to exceed the elastic limit of said desired crosssection in tension, continuously pulling said strip through the die means by application of tensile force to one end of the strip while applying such additional compressive force on the strip with'said die means as necessary to increase the resistance to passage of the strip therethrough to a value exceeding the said elastic limit and simultaneously bending the portion of said strip which is in tension adjacent saidcnd to substantially the final configuration of one of said workpieces then transferring the applicationbf said tensile force to a section of the unbent strip adjacent said portion and finally severing said bentportion from the strip.

3. The method of. forming elongatedrbent workpieces of a desired cross-section, com-prising pulling a strip of flat stock between rollers defining a passage of said cross-section, by securing an end of the strip which has passed between said rollers to a peripheral surface conforming to the bent configuration of a workpiece and rotating said surface with the strip extendingtherefrorn in a generally tangential direction, while applying sufficient pressure with said rollers against the strip to resist rotation of the strip with said surface. with a force exceeding the elastic limit of said cross-section in tensionyand, after the strip has rotated with said surface for a distance from said end equal to the length of a workpiece, additionally securing the strip on said surface at a distance from the end of the strip equal to a workpiece length, then severing the strip on said surface at said distance, and then releasing the severed portion of the strip.

4. Apparatus. for forming successive elongated bent workpieces having a desired cross-section, comprising die means having surfaces coacting upon pulling a strip of stock of predetermined cross-section therebetween to alter its cross section to said desired cross-section and resist passage of the strip therebetween with a force stressing said desired cross-section to substantially its elastic limit in tension, a member having an elongated surface conforming to the bent configuration of said workpieces, means for releasably attaching the pulled end of the strip to said conforming surface, means for moving said member in the direction to pull the attached strip longitudinally between said die meanssurfaces and wrap the strip longitudinally about said conforming surface, means for further releasably attaching the strip to said conforming surface at a distance from said end of the strip slightly greater than the length of a workpiece, and means for severing the strip on said conforming surface at a distance from said end equal to the length of a workpiece.

5. The apparatus of claim 4, together with a support fixed against movement with said member, and means on said support operative to sequentially actuate said attaching means and severing means in response to movement of said member.

6. Apparatus for forming elongated bent workpieces having a desired cross-section, comprising die means having surfaces adapted to coact upon passage of a strip of stock of predetermined cross-section therebetween to alter said predetermined cross-section to said desired cross-section and to oppose said strip being pulled therebetween with a force stressing said desired cross-section to a value intermediate its elastic and ultimate tensile limits, a rotatable member having a surface extending therearound for bending said strip after passage between said die surfaces, means journaling said member for rotation including a fixed support, strip attaching means carried by said member and movable thereon between a position attaching the strip to said bending surface for rotation with said member and a released position, means located on said support and operative in response to rotation of said member to a preselected position to move said attaching means to its strip attaching position, strip severing means located on said member, means located on said support and operative in response to further rotation of said member a predetermined extent beyond said preselected position to actuate said severing means to sever the bent workpiece from the strip, means located on said support and operative in response to rotation of said member a further predetermined extent beyond said preselected position to move said attaching means to its released position, and means for rotating said member.

7. The apparatus of claim 6, together with a second strip attaching means and a second strip severing means carried by said member and spaced diametrically opposite thereon from said first named strip attaching means and strip severing means, respectively, and operative respectively by the same means operative to actuate said first named strip attaching means and strip severing means.

8. Apparatus for rolling and stretch bending workpieces of a desired cross-section, comprising a pair of rollers having strip rolling surfaces defining a passage of said cross-section, said rollers being adjustably movable toward and away from each other to resist the strip being pulled therebetween with a force exceeding the elastic limit of said cross-section in tension, means for applying sufficient force to that end of the strip which has passed between the rollers to pull the strip therebetween with the rollers adjusted to apply said resisting force on the strip and for simultaneously bending a portion of the strip adjacent said end to the configuration of a workpiece, said means including a rotatable member having a peripheral surface of the configuration of a bent workpiece, clamp means for releasably securing the strip to said surface including two clamps carried by said member and spaced from each other a distance around said surface equal to the length of a workpiece, each operable between a first position securing the strip to said surface and 21 released position, and fixed cam means operable to actuate and release said clamps in timed relation to rotation of said member, and strip severing means including a strip shearable element carried by said member adjacent each said clamp and fixed cam means operable to actuate said elements to shear the strip, said last named cam means being located for actuation of the shearable element following actuation of its adjacent clamp to said first position.

References Cited in the file of this patent UNITED STATES PATENTS 321,019 Green June 30, 1885 1,459,660 Felten June 19, 1923 1,837,196 Bergest et al. Dec. 22, 1931 2,043,792 Blank et al. J11ne 9, 1936 2,073,174 Potter Mar. 9, 1937 2,288,855 Steinmayer et al. July 7, 1942 2,305,354 Kellogg et al Dec. 15, 1942 2,393,804 Nigro Jan. 29, 1946 2,649,336 Anderson Aug. 18, 1953 

1. THE METHOD OF FORMING SUCCESSIVE ELONGATED BENT WORKPIECES HAVING A DESIRED CROSS-SECTION, COMPRISING PULLING A STRIP OF STOCK OF OTHER THAN SAID DESIRED CROSSSECTION BETWEEN TWO MEMBERS COOPERAABLE IN RESPONSE TO MOVEMENT OF SAID STRIP THEREBETWEEN TO ALTER THE CROSSSECTION OF THE STRIP TO SAID DESIRED CROSS-SECTION, APPLYING SUFFICIENT FORCE TO SAID STRIP IN OPPOSITION TO SAID MOVEMENT TO STRESS SAID DESIRED CROSS-SECTION TO SUBSTANTIALLY ITS ELASTIC LIMIT IN TENSION, BENDING SUCCESSIVE PORTIONS OF STRIP WHICH HAVE PASSED BETWEEN SAID MEMBERS AND WHILE THEY ARE UNDER SAID TENSION TO SUBSTANTIALLY THEIR FINAL CONFIGURATION, AND THEN RELIEVING THE SUCCESESIVE BENT PORTIONS OF SAID TENSION AND SEVERING THEM FROM THE STRIP.
 6. APPARATUS FOR FORMING ELONGATED BENT WORKPIECES HAVING A DESIRED CROSS-SECTION, COMPRISING DIE MEANS HAVING SURFACES ADAPTED TO COACT UPON PASSAGE OF A STRIP OF STOCK OF PREDETERMINED CROSS-SECTION THEREBETWEEN TO ALTER SAID PREDETERMINED CROSS-SECTION TO SAID DESIRED CROSS-SECTION AND TO OPPOSITE SAID STRIP BEING PULLED THEREBETWEEN WITH A FORCE STRESSING SAID DESIRED CROSS-SECTION TO A VALUE INTERMEDIATE ITS ELASTIC AND ULTIMATE TENSILE LIMITS, A ROTATABLE MEMBER HAVING A SURFACE EXTENDING THEREAROUND FOR BENDING SAID STRIP AFTER PASSAGE BETWEEN SAID DIE SURFACES, MEANS JOURNALING SAID MEMBER FOR ROTATION INCLUDING A FIXED SUPPORT, STRIP ATTACHING MEANS CARRIED BY SAID MEMBER AND MOVABLE THEREON BETWEEN A POSITION ATTACHING THE STRIP TO SAID BENDING SURFACE FOR ROTATION WITH SAID MEMBER AND A RELEASED POSITION, MEANS LOCATED ON SAID SUPPORT AND OPERATIVE IN RESPONSE TO ROTATION OF SAID MEMBER TO A PRESELECTED POSITION TO MOVE SAID ATTACHING MEANS TO ITS STRIP ATTACHING POSITION, STRIP SEVERING MEANS LOCATED ON SAID MEMBER, MEANS LOCATED ON SAID SUPPORT AND OPERATIVE IN RESPONSE TO FURTHER ROTATION OF SAID MEMBER A PREDETERMINED EXTENT BEYOND SAID PRESELECTED POSITION TO ACTUATE SAID SEVERING MEANS TO SEVER THE BENT WORKPIECE FROM THE STRIP, MEANS LOCATED ON SAID SUPPORT AND OPERATIVE IN RESPONSE TO ROTATION OF SAID MEMBER A FURTHER PREDETERMINED EXTENT BEYOND SAID PRESELECTED POSITION TO MOVE SAID ATTACHING MEANS TO ITS RELEASED POSITION, AND MEANS FOR ROTATING SAID MEMBER. 